As a film or sheet used for wrapping of foods, medicinal products, daily groceries and the like, molded articles obtained by extrusion-molding an ethylene based polymer are often used. Among ethylene based polymers, a linear copolymer composed of ethylene and α-olefin, so called linear low density polyethylene, is excellent in impact strength as compared with a high pressure low density polyethylene having long chain branch. Thus, a wrapping material composed of a linear low density polyethylene can be made thinner as compared with a wrapping material composed of a high pressure low density polyethylene.
However, as compared with a high pressure low density polyethylene, a linear low density polyethylene has lower melt tension, and manifests wrinkling of a film by vibration of a bubble in blown film molding, and increase in the distribution of a film thickness (hereinafter, there are referred to as moldability). Therefore, methods for improving moldability are investigated, and there is suggested a polymer composition obtained by blending 5 to 30% by weight of a high pressure low density polyethylene into a linear low density polyethylene (for example, Japanese Patent Publication of Examined Application (JP-B) No. 62-3177, Japanese Patent Application Laid-Open (JP-A) No. 11-181173). This polymer composition, however, shows lower strength as compared with a linear low density polyethylene, in some cases.
Recently, investigations of a polyethylene production catalyst have progressed, and it has been reported that an ethylene-α-olefin copolymer having long chain branch excellent in strength and moldability is obtained by polymerizing ethylene and α-olefin with a specific metallocene catalyst (for example, JP-A No. 2005-97481).
However, also the above-described ethylene-α-olefin copolymer having long chain branch is not sufficiently satisfactory in strength and moldability.